A number of active joysticks or haptic interfaces (interfaces capable of generating kinesthetic and tactile feedback to the user) have been proposed for virtual environments and teleoperation systems.
Attention is directed to Stocco, L., Salcudean, S. E., "A coarse-fine approach to force-reflecting hand-controller design," in Proc. 1996 IEEE Intl. Conf. Rob. Aut. Minneapolis, Minn., pp..about.404-410, Apr. 22-28 1996. for a detailed survey, and to Hayward, V., Astley, O. R., "Performance measures for haptic interfaces," in Proc. ISRR, p..about.(12 pages), 1995. for performance measures.
The need for high acceleration in haptic computer-user interfaces has been demonstrated in many studies and seems to have been accepted by designers. Although most reported designs have translational workspaces that exceed a cube with 10 cm sides, it has not been shown that a workspace of this magnitude is really needed. Indeed, for desk-top computing, input devices such as mice, trackballs or joysticks are commonplace. These devices have relatively small motion ranges to avoid tiring the operator. Furthermore, designing high acceleration devices over large workspaces is a non-trivial task requiring expensive actuators, transmissions and joints.
As an alternative, the use of a small workspace haptic device in rate mode or combined position/rate mode has been proposed and demonstrated see Salcudean, S. E., Wong, N. M., Hollis, R. L., "Design and Control of a Force-Reflecting Teleoperation System with Magnetically Levitated Master and Wrist," IEEE Trans. Rob. Aut., vol..about.11, pp..about.844-858, December 1995.
Magnetically levitated (maglev) Lorentz devices such as those described in Hollis, R. L., Salcudean, S. E., Allan, P. A., "A six degree-of-freedom magnetically levitated variable compliance fine motion wrist: Design, modeling and control," IEEE Trans. Rob. Aut., vol..about.7, pp..about.320-332, June 1991 and U.S. Pat. No. 5,146,566, issued September, 1992 to Hollis, R. L. and Salcudean S. E are suitable small-motion haptic interfaces because of their low mass, lack of friction and backlash, and high acceleration ability. Devices have been built at IBM (see Hollis, R. L., Salcudean, S. E., Allan, P. A., "A six degree-of-freedom magnetically levitated variable compliance fine motion wrist: Design, modeling and control," IEEE Trans. Rob. Aut., vol..about.7, pp..about.320-332, June 1991); at University of British Columbia (see Salcudean, S. E., Wong, N. M., Hollis, R. L., referred to above), and at Carnegie-Mellon University (see Berkelman, P. J., Butler, Z. H., Hollis, R. L., "Design of a hemispherical magnetic levitation haptic interface device," in Proc. 1996 ASME IMECE, vol..about.DSC-58, Nov. 17-22 1996).
In such devices magnetic forces are used to actively levitate a rigid mass or flotor to which the handle manipulated by the operator is attached. These devices share the following three subsystems:
(i) an actuation system consisting of at least six flat voice-coil or Lorentz actuators, PA1 (ii) an optical position sensing system consisting of infrared linear light rays projecting from light-emitting diodes or lasers onto two-dimensional lateral effect photodetectors or position sensing diodes, PA1 (iii) a control system that commands forces and torques to the actuation system based on the desired and sensed position, the desired force and the desired relationship between force and position (mechanical impedance).
A number of applications of maglev devices are described in the survey paper Hollis, R. L., Salcudean, S. E., "Lorentz levitation technology: a new approach to fine motion robotics, teleoperation, haptic interfaces, and vibration isolation," in Proc. 5th Intl. Symp. on Robotics Research, (Hidden Valley, Pa.), p..about.(18 pages), Oct. 1-4 1993.
U.S. Pat. No. 5,790,108 issued to Salcudean et al. on Aug. 4, 1998 describes a specific application of the Lorentz voice coils in a hand controller.